1. NUCLEAR CHEMISTRY
NUCLEONS – The particles found in the nucleus
Protons (+)
Neutrons (0)
Mass Number (A) 
Atomic Number (Z)  Hg 80
196
Protons: 80
Neutrons: = 116
2C-1 (of 15)

2. STABILITY SERIES
STABLE ISOTOPES – Atoms with nuclei that last forever
RADIOACTIVE ISOTOPES – Atoms with nuclei that eventually break down to more stable nuclei
Isotopes are stable when their nuclei have enough neutrons to minimize proton-proton repulsion
(a) For Z < 20
Stable nuclei need 1 neutron per proton
(b) For Z > 20
Stable nuclei approach needing 1.5 neutrons per proton
2C-2

3. Stable 200Hg atom:
120 n, 80 p
1.5:1 ratio
Stable 16O atom:
8 n, 8 p
(1:1 ratio)
2C-3

4. NUCLEAR DECAY
Each radioactive isotope undergoes nuclear decay at its own unique rate
HALF-LIFE (t1/2) – The time required for half of the radioactive isotopes in a sample to decay
The shorter the half-life, the more unstable the isotope
Half-life for 131I = 60 days
At 0 days:
At 60 days:
At 120 days:
At 180 days:
At 240 days:
16 125I atoms
8 125I atoms
4 125I atoms
2 125I atoms
1 125I atom
2C-4

5. Half-life for 14C = 5,730 years
At 0 yrs:
At 5,730 yrs:
At 11,460 yrs:
At 17,190 yrs:
At 22,920 yrs:
16 14C atoms
8 14C atoms
4 14C atoms
2 14C atoms
1 14C atom
How old is an axe with an elk antler sleeve if it has 25% the 14C content of antlers in living elks?
11,460 years old
2C-5

6. NUCLEAR DECAY
(1) ALPHA DECAY (α) – The release of a helium-4 nucleus (4He2+) from a nucleus to become more stable
α’s are emitted from radioactive isotopes with A > 200
U → 92
238
He + 2 4 Th 90
234
A and Z are always conserved in nuclear changes
Po → 84
207
He + 2 4 Pb 82
203
Alpha particles can be stopped by the outermost layer of skin
2C-6

7. (2) BETA MINUS DECAY (β-) – The release of an electron from a nucleus to become more stable
β-’s are emitted from radioactive isotopes with too many neutrons
Essentially a neutron is decaying into a proton plus an electron
C → 6 14
e + -1 N 7 14
K → 19 40
e + -1 Ca 20 40
Beta particles penetrate about 1 cm into the body
2C-7

8. (3) POSITRON DECAY (β+) – The release of an electron with a positive charge from a nucleus to become more stable
β+’s are emitted from radioactive isotopes with too many protons
Essentially a proton decays into a neutron and an antimatter electron
C → 6 11
e + 1 B 5 11
Ca → 20 38
e + 1 K 19 38
2C-8

9. (4) GAMMA DECAY (γ) – The release of any high energy photon of electromagnetic radiation
γ-’s are emitted along with other forms of decay
Gamma rays are deeply penetrating
2C-9

10. Usually very radioactive
(6) SPONTANEOUS FISSION – When a large nucleus (Z > 80) breaks into two, approximately equal halves
Several neutrons, and lots of energy are released when nuclei fission
U → 92
239
Ru + 44
116
Cd + 48
120
3 n 1
U → 92
239
Rh + 45
118
Ag + 47
119
2 n 1
Daughter Products
Usually very radioactive
2C-10

11. U + n → U 235 1 236 92 92 NUCLEAR REACTORS
Nuclear reactions release over 100 times more energy than chemical reactions
235U is used as a fuel
U + 92
235
n → 1 U 92
236
236U decays by spontaneous fission
CHAIN REACTION – When at least one neutron per fission produces a new 236U
2C-11

12. Not enough neutrons captured for a chain reaction
Just enough neutrons captured to maintain a chain reaction
So many neutrons captured the chain reaction is an explosion
CRITICAL MASS – The minimum amount of 235U needed to support a chain reaction
2C-12

13. Water – Acts as a MODERATOR to slow down the neutrons,
as a COOLANT to keep the reactor core from overheating,
and as PROTECTION because it absorbs radiation
Cd or B Control Rods – Absorb neutrons to control the rate of the chain reaction
Fuel Elements – Metal casings containing 235U
Reactor Core
2C-13

14. San Onofre Nuclear Generating Station
Heat from the nuclear fission boils water, and steam turns a turbine, which produces electricity
Used up full elements contain radioactive daughter products, which must be disposed of safely
2C-14

15. FUSION – The combining of small nuclei to produce large nuclei
Fusion occurs in stars
4 H → 1 He 2 4
Very high temperatures or pressure are needed to overcome the repulsion of the positive hydrogen nuclei
Fusion releases much more energy than fission
2C-15